Self-calibrating Ratiometric Fluorescence Detection of Silver Ions by a White-light-emitting Probe.

Ratiometric fluorescence sensing provides built-in self-calibration against fluctuations in excitation intensity and environmental conditions, yet it commonly demands complex design of dual-emission materials. Herein, we present an exceptionally simple strategy: physically mixing separately synthesized blue-emitting carbon dots and yellow-emitting carbon dots to yield a white-light-emitting composite (CA/OPD-CDs). Under single excitation at 256 nm, the mixture displays three well-resolved emission peaks at 340, 440, and 560 nm. The 560 nm peak is selectively and efficiently quenched by Ag⁺ ions, whereas the 440 nm peak remains stable, enabling self-calibrated ratiometric detection via the intensity ratio F₅₆₀/F₄₄₀. The probe exhibits a linear response to Ag⁺ from 0 to 11 µM (R² = 0.996) with a detection limit of 80 nM, well below the WHO drinking water guideline. Outstanding selectivity over 13 other metal ions is demonstrated. UV-Vis absorption and fluorescence lifetime measurements confirm a static quenching mechanism through ground-state complex formation. The method was successfully applied to Ag⁺ determination in tap water, achieving recoveries of 97.9-106.5%. This work demonstrates that simple physical blending of distinct carbon dots can replace intricate one-pot syntheses to generate powerful self-calibrating ratiometric sensors, offering a facile and generalizable platform for analytical applications.